Open top hopper and open top gondola railroad cars are specifically designed to transport, load, and unload bulk commodities, such as mineral ores and coal. Such cars generally have a number of interior struts with irregular shapes and surfaces. This interior bracing provides necessary support and strength to the side walls of the railcar. Most railcars used in hauling coal and the like include a so-called center sill. This center sill is generally a stiff I-beam or the like which extends from one endwall of a railcar to the other adjacent the floor of the car, or at least from one truck of the railcar to the other.
Support bracing may extend upward from the car's floor or center sill as a plurality of paired struts which are angled toward the sidewalls away from the center sill to define a number of V-shaped supports. In other railcar designs, the braces may extend horizontally directly from one side wall of the car to the other, in which case a plurality of such struts may be staggered along the length of the railcar, with some of the braces being disposed adjacent the floor and others being carried closer to the tops of the sidewalls. In yet other railcars, some combination of these approaches is used to provide lateral strength to the side walls of the car, such as where a straight brace extends from the top of the center sill generally horizontally to both sidewalls and a V-shaped pair of supports is associated with the straight brace.
Present car designs have an interior bracing configuration which is very often extensive and staggered, giving consideration only to the physical support required by the car's side walls for transportation of the bulk commodity for which the car is intended. Railcars are generally configured within a range of overall lengths accepted in given industries to meet industry-specific loading, unloading, and volumetric requirements. In many applications, the floor is irregular. For instance, a hopper car may have a series of V-shaped depressions in the floor having sealable openings through which coal or other bulk commodities may be discharged. In some rotary dump cars, the floor includes a pair of elongate arcuate depressions, with one such depression being disposed on either side of and extending adjacent the center sill, and the endwalls of the car may meet the floor in a relatively gentle curve rather than substantially perpendicularly.
In U.S. patent application Ser. No. 910,900 filed Jul. 8, 1982 in the name of the inventor of the present invention (the teachings of which are incorporated herein by reference), a system for efficiently utilizing railcars devoted to hauling certain bulk commodities, such as coal, into dual-use railcars. This is accomplished by the use of one or more bladders in each railcar. These bladders are adapted to carry a flowable material so that one commodity (e.g. coal) can be hauled by the railcar in one direction in a standard configuration and a flowable second commodity, such as fly ash, can be hauled in the railcar on the return trip. Presently, commercially operated coal cars run in a circuit between a mine and a drop off site, such as a coal-fired power plant, and are forced to deadhead without any cargo on the return trip from the drop off site to the mine. Use of bladders as taught in U.S. patent application Ser. No. 910,900 permits a railroad operator to haul freight on the return trip by placing a different commodity in bladders and carrying those bladders in the car.
Bladders suitable for use in such an application are commercially available, such as those sold under the tradename Fabribin by the American Fuel Cell and Coated Fabrics Company. These bladders are available in a variety of sizes, ranging from relatively small capacity vessels to bladders capable of holding 20,000 pounds or more of a flowable commodity. As a railcar containing bladders filled with flowable commodities moves from one location to another, the train will generally have to vary its speed from time to time, e.g. when the train goes through a metropolitan area or travels along a curvaceous path.
This speeding up and slowing down causes the load in the railcar to be urged back and forth in the railcars under inertia. Similar forces act on the commodity in a railcar as it travels along curves in the track, when trains switch tracks and when coupling cars together. With a relatively bulky, poorly flowing material such as standard coal, the contents of the car will not tend to shift from side to side or from one end of the car to the other despite these forces. With a more flowable commodity, though, this can be a problem.
When a single bladder is used in a railcar, the bladder will tend to sway under the changes in direction and speed of the railcar. However, this does not tend to be a problem if the bladder is supported and space is provided between the bladder and the endwalls. When a series of bladders are installed in a railcar extending substantially along the entire length of the car, though, the shifting of the load can be problematic.
When a train appreciably accelerates or decelerates, the contents of the bladder at one end will flow rearwardly or forwardly, respectively, due to inertia. If this first bladder is allowed to contact another bladder, the contents of the second bladder will move not only due to inertia but also in response to the force of the first bladder acting against the second bladder and the contents of the second bladder will react more noticeably and rapidly than the contents of the first bladder. If this process is carried along a series of three or four bladders, the resultant accumulated force can be quite strong. In some circumstances, this "surge" of force could, in theory, be great enough to rip an endwall away from the rest of the car, particularly as most railcars used for hauling coal and the like do not have any direct connection between the two endwalls.
Open top gondolas and hoppers for carrying bulk commodities (e.g. coal) are not presently designed to expediently and efficiently accommodate bladders for transport. The staggered bracing configurations of such railcars outlined above can totally preclude, or at least reduce, the number and/or size of bladders which may be effectively used in the car.
At least one railcar has been designed specifically for the transport of bladders. These low-sided gondola cars have interior walls to compartmentalize the car into areas designed to snugly receive several bladders and a continuous flat floor to provide an even plane on which they will rest. These railcars are not adapted to transport coal or similar bulk commodities for use in industry-standard procedures because they do not meet the necessary volume, loading, and unloading parameters. These cars' interior wall design, to secure the bladders during transport, completely compartmentalizes the cars making this design deficient for use in coal cars. For example, when coal is flood loaded into a car at 100 tons or more per minute, it puts great stress on the walls of the car and coal must be allowed to flow throughout the volume of the car for accurate and effective loading. The braces and the center sill of current coal car designs are adapted to provide strength to the railcar structure to withstand these forces (as well as torsional and flexural stresses during transport), yet allow the coal or other such commodity to readily flow around the bracing to rapidly and easily fill the railcar.
The interior wall design of this bladder carrying railcar most likely would be unable to withstand the physical forces because the compartment walls preclude the coal from flowing throughout the car. Also, freezing of coal in railcars during winter transport is a major problem in the industry. The bladder railcars' compartments defined by these interior wills would also enhance the undesirable effect of frozen coal in the car through compartmentalization.
By their very construction, tanker cars are unsuitable for hauling anything but fluids. Similarly, open topped hopper cars are not very useful for hauling anything but granular commodities, and bladder gondolas are ill suited for transporting anything but bladders. All three types of railcars have dedicated use construction, which means such cars frequently carry loads only in one direction, resulting in high operating expenses for the railroad. These costs include fuel for transporting empty cars, and high capital costs for single purpose cars which ride the mils empty half the time. This creates a significant under-utilization of railroad equipment and capital.
Furthermore, from time to time with changes in market demands for materials and their associated railcars, there is significant oversupply or under demand for railcars with changing markets. Present car configurations provide the railroad with minimum car use flexibility to respond to these changing market dynamics during the cars' service life, which is often fifty years.
Bladders are such as those mentioned above are a desirable way to utilize railcars designed to carry a bulk commodity in one direction and carry a different material which requires containment, such as waste products including coal fly ash, biosolids (sewage sludge), municipal solid waste (MSW) or commodities such as lime or petrochemical fertilizers, on the return trip. As explained earlier, though, bladders are not readily accepted by the present configurations of most coal cars and the volume of the car which can be filled with bladders is somewhat limited. Bladders have been transported on converted flatbed/low side gondola railcars in the past, but these cars are not readily adaptable to handling coal, mineral ores and similar bulk materials.
Thus, it would be desirable to provide a railcar which can be used to haul both bulk commodities such as coal and liquids or other flowable materials. In particular, such a design would optimally permit the bladder or bladders to be readily removed from the cargo hold of the railcar so that the car may be filled, and possibly emptied at existing rates, with existing equipment through an open top, yet accommodate bladders for hauling other flowable materials.